Synthesis of a trisaccharide repeat of the zwitterionic Sp1 capsular polysaccharide utilizing 2-azido-4-benzylamino-4N,3-O-carbonyl-2,4,6-trideoxy-d-galactopyranosyl trichloroacetimidate

• Synthesis of a trisaccharide repeat of the zwitterionic Sp1 polysaccharide.
• A versatile diamino trideoxyhexose donor.
• Differentiation of C2 and C4 amino groups.
• Post assembly creation of two uronic acids by TEMPO oxidation.
• Base cleavage of oxazolidinone.

2-Azido-4-benzylamino-4N,3-O-carbonyl-2,4,6-trideoxy-d-galactopyranosyl trichloroacetimidate 2 conveniently prepared in six steps from 6-deoxy-d-glucal glycosylated a selectively protected α1,3 linked methyl galabioside to afford the trisaccharide skeleton of a repeating unit of the Sp1 zwitterionic capsular polysaccharide. Lithium hydroxide hydrolysis of the 3,4-cyclic carbamate permitted the creation of a 2-acetamido-4-amino-2,4,6-trideoxygalactose residue. Selective cleavage of p-methoxybenzyl ethers by trifluoroacetic acid gave a selectively deprotected trisaccharide with two hydroxymethyl groups that were oxidized by the TEMPO reagent to afford access to trisaccharide glycoside 1 containing 2-acetamido-4-amino-2,4,6-trideoxygalactose and two galacturonic acid residues.

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